In pipe lines to handle hazardous gas, for example poisonous, inflammable or corrosive gas for making semiconductors, double tube having inner tube and outer tube is used for preventing gas leakage.
Valve unit used in such pipe lines is also required to have gas leakage preventing mechanism.
FIG. 2 shows a conventional valve unit of this type, as manufactured and sold by Valex Corporation, 6080 Leland Street, Ventura, Calif.
In the piping P, double tube 3 having an inner tube 1 and an outer tube 2 is used. In the inner tube 1, hazardous gas flows, while vacuum is applied to the conduit 2a formed between the inner tube 1 and the outer tube 2, or an inert gas of nitrogen gas and such like flows in the conduit 2a.
A valve unit installed in the piping P, a cover casing 5 for covering the valve unit 4 is used for preventing hazardous gas leakage to the environment.
The cover casing 5 is composed of an under body 5a and an upper body 5b. Apertures 5d formed in the under body 5a are welded to the outer tubes 2,2 of the double tubes 3,3.
The upper body 5b has an aperture through which a valve shaft 4a of the valve unit 4 is assembled with seal rings 4d. On top of the valve shaft 4a is attached a knob 4b for controlling the valve unit 4.
Under body 5a and upper body 5b are tightened together with a fastener 6 with proper seal means.
In case of the leakage of the hazardous gas from the valve unit 4, the gas will fill in the cover 5. Then the gas filled in the cover 5 is lead to the conduit 2a of the double tube 3, and sent to a device to handle the hazardous gas.
In this type of conventional valve unit, all the valve body is covered by the cover, thereby the size of the valve unit becomes incompact.